It is well-known that in conventional inkjet recording ink is sprayed through a minute nozzle onto paper or other recording media to which it adheres to execute the designated recording job. Named after the differences in their discharge mechanisms, this system is further divided into two distinct ink droplet discharge systems (herein referred to as recording heads) that use this method—the thermovalve system and the Kaiser system.
In the thermovalve system, ink instantaneously heated and boiled near the nozzle is discharged. In the thermovalve system, however, the heater component that generates heat has a short life-span, and because calorific (heating) value increases relative to discharge frequency, it is not suited to high-speed continuous recording.
Named after its inventor, in the Kaiser system, the rear part of the nozzle is equipped with an ink compression chamber and a piezoelectric element that functions as the transformable wall of the compression chamber, such that applying voltage to transform the piezoelectric element causes ink discharge. The principle of the recording head in the Kaiser system has already been disclosed in patent document 1 (Published examined application no. 1978-12138, FIGS. 2 and 3) It has few of the drawbacks pointed out in the thermovalve system, and is beneficial to the realization of high-speed and continuous recording.
Due to the advantages of high-speed and continuous recording, the Kaiser system is normally adopted.
There are 2 types of recording heads used in the Kaiser system—the edge shooter recording head and the side shooter recording head. FIG. 10 is a schematic drawing explaining the differences between edge shooter recording head 110 and side shooter recording head 120. In the edge shooter, the substrate is used vertically, while the side shooter uses it horizontally. For this reason, the edge shooter projected area on paper or other recording media 130 is significantly smaller than that of the side shooter.
The following is a detailed explanation of edge shooter recording head and the side shooter recording head.
The edge shooter recording head shall be explained first. FIG. 11 is a structural diagram of the single-sided edge shooter recording head, where 11(a) is a front elevational view, 11(b) is a bottom view and 11(c) is a cross-sectional view of XIc-XIc.
The single-sided type edge shooter recording head is equipped with flow channel substrate 1, nozzle 2, ink compression chamber 3, aperture flow channel 4, ink tank 5, ink supply port 6, diaphragm 7 and piezoelectric element 8.
One side (the top side in 11(b)) of Flow channel substrate 1, a substrate made from silicon wafer, glass or metal plate, etc, is processed using etching or other mechanical methods to produce canaliform structures for nozzle 2, ink compression chamber 3, aperture flow channel 4, etc and ink tank 5 that connects them all. In addition, ink tank 5 is linked via ink supply port 6 to the ink supply well not shown in the diagram. In the edge shooter recording head where, after covering and integrating diaphragm 7 with the surface of the processed side of flow channel substrate 1, electric device conversion element piezoelectric element 8 is bonded to the surface of the side opposite diaphragm 7 at a location corresponding to that of ink compression chamber 3. Nozzle 2 is mounted to the edge of the substrate that corresponds to the direction perpendicular to the direction of distortion caused by piezoelectric element in ink compression chamber 3. The device is equipped with 20 units of nozzle 2.
When operating the single-sided edge shooter recording head, applying pulse form voltage to piezoelectric element 8 causes diaphragm 7 to distort, and when the distortion is recognized by ink compression chamber 3, the volume of ink compression 3 is rapidly reduced and ink droplets 150 amounting to a portion of the ink equivalent to this reduced volume are discharged from nozzle 2 to adhere to and execute the designated print job on the recording media not shown.
FIG. 12 is a structural diagram of the double-sided edge shooter recording head, where 12(a) is a front elevational view, 12(b) is a bottom view and 12(c) is a cross-sectional view of XIIc-XIIc.
In comparison to the single-sided edge shooter recording head in which flow channels are formed only on one side of flow channel substrate 1, the double-sided edge shooter recording head shown in FIG. 12 is equipped with flow channels formed in the same way on both sides (the top and bottom surfaces in 12(b)) of flow channel substrate 1. As a result, 40 units, 2 times the normal 20 nozzle(s) 2, can be formed on the same substrate.
Next is an explanation of the side shooter recording head. FIG. 13 is a structural diagram of the side-shooter type recording head, where 13(a) is a front elevational view, and 13(b) is a cross-sectional view of XIIIb-XIIIb.
The side shooter recording head is equipped with cavity plate 11, ink compression chamber 12, aperture flow channel 13, ink tank 14, nozzle plate 15, diaphragm 16, nozzle 17, piezoelectric element 18, and ink supply port 19.
Cavity plate 11 is a metal, glass, ceramic, plastic, etc substrate that is equipped with ink compression chamber 12, aperture flow channel 13, and ink tank 14 formed using etching or other mechanical processing methods, and on each side of which nozzle plate 15 and diaphragm 16 are layered and integrated using an adhesive, diffusion bonding, or other method.
Ink flow channel 14 is common to the multiple ink compression chambers 12 formed on cavity plate 11 and extends to both sides along these ink compression chambers 12. Each ink compression chamber 12 is connected by aperture flow channel 13 to ink supply channel 14. In addition, one end of ink supply channel 14 is connected to ink supply port 19. Nozzle plate 15 is equipped with nozzle 17 such that it is formed perpendicularly to ink compression chamber 12 to which it communicates.
Furthermore, electric device conversion element piezoelectric element 18 is adhered or bonded to the outer periphery of diaphragm 16 that corresponds to ink compression chamber 12. This kind of side shooter recording head is positioned in the same direction as the displacement direction of piezoelectric element 18 and diaphragm 16. The device is equipped with 20 units of nozzle 17.
When operating the side shooter recording head, applying pulse-form voltage to piezoelectric element 18 displaces diaphragm 16 inward, thus decreasing the volume inside ink compression chamber 12. As a result of this, the amount of ink that corresponds to the displaced volume is discharged from nozzle 17 to record job data on the recording media not shown.
The following is a comparison of the recording density of the edge shooter recording head and the side shooter recording head. Here, we will consider the issue of mount density as a factor when increasing the number of nozzles; in other words, the number of nozzles that can be formed on the surface of a single substrate.
In order to attain the same discharge performance (discharge amount, discharge speed, discharge frequency) for both the edge shooter and the side shooter, recording heads, it is necessary to provide the same level of driving force in each system, but when using piezoelectric elements for both systems, the amount of drive force achievable is basically determined by the surface area of the compression chamber. Since form is determined by the need for air bubble removability and a lead wire extraction method and so on, both head types are generally shaped like rectangular strips. As a result, the surface area of their compression chambers are approximately the same.
Furthermore, as can be seen in FIG. 12, the edge shooter recording head is equipped with head functions on both sides of the head substrate. In comparison to this, the side shooter recording head cannot be configured with components on both sides since its compression and nozzle components are located on different surfaces. For this reason the edge shooter recording head is highly beneficial from the perspective of enhancement of nozzle density. Therefore, when attempting to increase the number of nozzles by lining up multiple nozzles on the head substrate, the edge shooter type provides a more highly advantageous structure than the side shooter type.
Most current inkjet recording device recording heads employ a method of scanning (sweeping across) the recording media widthwise. The reason that this type of scanning is necessary is that the head is equipped with a limited number of nozzles and cannot cover the entire width of the recording media at once. For example, to record data to a sheet of A4 paper (width 210 mm) at a dot recording density of 600 dpi with a fixed head would require a recording head equipped with 4961 (=210÷25.4×600) nozzles aligned at intervals of 1/600 inch (=42.33 μm).
It is extremely difficult to produce a single sheet of substrate mounted with a recording head equipped with such as large amount of nozzles. To realize this, a semiconductor manufacturing method appropriate for precision processing is generally used. However, to this end, it is necessary to use a material of proportionally greater size than the 210 mm-wide recording width, such as a 300 mm-diameter silicon wafer, but the equipment needed to handle such large diameter wafers is terribly expensive, and from the perspective of yield, not very practical.
Therefore, the method of mounting a single sheet of substrate with several tens to several hundreds of recording heads that can be easily attached to achieve scanning is normally adopted. This head scanning method, however is highly disadvantageous to recording speed since the back and forth traveling of the head requires repeated acceleration and deceleration.
Thus, in order to solve the abovementioned problems, in patent document 2 (Bulletin No. 1996-300645 (FIGS. 1-3)), a long fixed inkjet recording head was disclosed where the number of nozzles desirable from the manufacturing perspective were configured on a single sheet of substrate in the edge shooter type configuration, after which this structure was aligned in the number required so as to eliminate the need to scan the head.
The configuration of on-demand inkjet recording devices is simple, but although it uses ink which is inexpensive and suited to colorization as a means of recording, its slow recording speed has set back its dissemination into the industrial fields that require high-speed printing.
In order to achieve greatly improved recording speed, it is desirable to employ a system in which the width of the target recording media is covered entirely by the recording head such that the recording head remains stationary while the recording media sweeps. However, because the number of nozzles on such a long recording head becomes so great, the density of nozzles above the surface of the recording media must be high and the head must be of a configuration that provides good production yield.
In the abovementioned patent document 2's inkjet recording head, all components except the nozzles are configured on separate substrates, but all of the nozzles are established on a single plate. Furthermore, individual substrates and the nozzle plate are integrated using an adhesive bonding agent, etc, so that if even one of the nozzles malfunctions, the entire length of the inkjet recording head must be replaced. Therefore, this structure presents the disadvantage of a highly unfavorable relationship between production yield and demand.
In response to this issue, this invention was developed in consideration of the abovementioned problems for the purpose of providing a long inkjet recording head that is easy to manufacture and that can realize high-speed continuous recording.